A steam channel connecting a steam turbine and a condenser in a steam turbine system uses an expansion joint for absorbing relative displacement between the steam turbine and the condenser. As the expansion joint, a bellows is often used, for example, as described in the following PTLs 1 and 2. In the bellows for this purpose, negative pressure is generated and steam at higher temperature (for example, 60° C. to 80° C.) than a room temperature flows. Thus, the bellows is made of stainless steel to ensure high airtightness and reliability.